drm/exynos: hdmi: Add CONFIG_OF and use of_match_ptr() macro

Add CONFIG_OF to compile conditionally. of_match_ptr eliminates having
an #ifdef returning NULL for the case when OF is disabled.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Inki Dae <inki.dae@samsung.com>